1. Field of the Invention
The present invention relates generally to the fields of molecular biology and protein biochemistry. More specifically, the present invention relates to p38MAPK inhibitor(s) and applications of p38MAPK inhibitor(s) in the treatment of hypercholesterolemia.
2. Description of the Related Art
Mitogen-activated protein kinases (MAPKs) are proline-directed serine-threonine-protein kinases that have important functions as mediators of cellular responses to a variety of extracellular stimuli (1-4). Three subgroups of the mitogen-activated protein kinase super-family have been clearly identified: the extracellularly responsive kinases (p42/44MAPK or ERK-1/2), the c-Jun N-terminal kinases (p46/54JNK) which are also known as the stress-activated protein kinases (SAPK), and the p38MAPK (also known as RK, Mxi-2, CSBP1/2 or HOG-1-related kinases).
Although the mitogen-activated protein kinase families are structurally related, they are generally activated by distinct extracellular stimuli through distinct upstream dual specificity kinases, thus comprising a series of separate mitogen-activated protein kinase cascades (5-7). The best known pathway, Raf/MAPK/ERK kinase-1/2 (MEK-1/2)/p42/44MAPK is typically strongly stimulated by growth factors and mitogenic stimuli, usually by means of a Ras-Raf-1-dependent cascade (8, 9). In contrast, the other two pathways, p38MAPK and p46/54JNK are primarily activated by cellular stresses, including heat and osmotic shock, UV irradiation, proinflammatory cytokines, and hypoxia/reoxygenation (10-16). Ten isoforms of p46/54JNK and four/isoforms of p38MAPK have been identified in mammalian cells (17-26). No physiological role has been associated with the difference in substrate affinity of the JNKs or p38MAPK. Dual specificity kinases that activate p46/54JNK are MAPK kinase 4 (MKK4/SEK-1) and MKK7, whereas MK3 and MKK6 have been identified as activators of p38MAPK, displaying some degree of selectivity for individual p38MAPK isoforms (26-32). MKK6 functions as an activating kinase for all known p38MAPK isoforms, whereas MK3 predominantly activates the isoform p38MAPKxcex4. Among the identified substrates of mitogen-activated protein kinases are a variety of transcription factors that become activated upon their phosphorylation (1, 4, 6, 33).
Since specific inhibitors of the p42/44MAPK and p38MAPK cascades were first described, they have been widely used t o investigate their involvement in intracellular signal transduction pathways. The flavone compound PD98059 (2-(2xe2x80x2-amino-3xe2x80x2-methoxyphenyl) oxanaphthalen-4-one) is a specific inhibitor of the mammalian MEK-1/2 and has been used extensively for investigating physiological function of p42/44MAPK pathway (34). The pyridinylimidazole compounds SB203580 (4-(4-Fluorophenyl)-2-(4-methylsulfinylphenyl)-5-(4-pyridyl) 1H-imidazole) and SB202190 (4-(4-Fluorophenyl)-2-(4-hydroxyphenyl)-5-(4-pyridyl) 1H-imidazole) are specific inhibitors for p38MAPK since they selectively inhibit both p38MAPK xcex1- and xcex2-isoforms, but not the xcex3- and xcex4-isoforms. In addition, they exhibit no significant effect upon other related kinases, including other members of the mitogen-activated protein kinase families and their upstream activators (17, 35). A role for the p38MAPK has previously been identified using these inhibitors in diverse cellular processes such as lipopolysaccharide- and tumor necrosis factor-xcex1 (TNF)-induced cytokine production (17, 36), ultraviolet-and anisomycin-induced c-jun and c-fos expression (37), interleukin (IL)-2 and IL-7-mediated T-cell proliferation (38), glutamate- (39) and B cell Ag receptor-induced apoptosis (40), fibroblast growth factor-, arsenite and UVC-mediated CREB/ATF-1 phosphorylation (41, 42).
Analysis of the signal transduction pathways using the above inhibitors revealed a critical role for p42/44MAPK activation in induction of LDL receptor gene expression by a variety of extracellular stimuli (43-45).
The prior art is deficient in the lack of understanding the role of p38MAPK in the regulation of the LDL receptor expression. Further, the prior art is deficient in the lack of effective means of applying p38MAPK inhibitors to treat hypercholesterolemia. The present invention fulfills this long-standing need and desire in the art.
The present invention addresses directly the physiological role of p38MAPK in the regulation of LDL receptor expression by using highly specific pharmacological and molecular tools. Results presented demonstrate that simple inhibition of the p38MAPK basal activity is sufficient to induce LDL receptor expression. Co-transfection studies established that SB202190-induced LDL receptor expression is mediated by the activation of p42/44MAPK resulting from the inhibition of p38MAPK xcex1-isoform. Therefore, in intact cells, p38MAPK negatively regulates the p42/44MAPK and the responses mediated by this kinase. It is speculated that cross-talk between these mitogen-activated protein kinases, which mediate the effects of numerous extracellular stimuli, could be crucial for controlling a wide array of biological processes.
In one embodiment of the present invention, there is provided a compound for inducing low density lipoprotein receptor expression, wherein the compound is a p38MAPK inhibitor or a compound that activates p42/44MAPK. The representative examples of such compounds are SB202190 and SB203580.
In another embodiment of the present invention, there is provided a method of inducing LDL receptor expression in a cell by administering to the cell a compound disclosed herein. The cell is either hepatic or nonhepatic. Preferably, the compound induces the LDL receptor expression by 6-8 fold and further reduces cholesterol level in the cell.
In still another embodiment of the present invention, there is provided a method of treating an individual having hypercholesterolemia by administering a compound disclosed herein. Preferably, the compound is administered at a concentration range of from about 1 xcexcM to about 100 xcexcM.
Other and further aspects, features, and advantages of the present invention will be apparent from the following description of the presently preferred embodiments of the invention given for the purpose of disclosure.